Control of hardening of steel



July 12, 1938 c. w. HANSELL CONTROL OF HARDENING OF STEEL Filed June 8, 1934 INVENTOR C.w. HANSELL BY MZ ATTORNEY Patented July l2, 1938 amavis coN'raor. or aanname or STEEL Clarence W. Hanse, Rocky Point, N. Y.,

to Radio Corporation of America,

tion of Delaware assigner a corpora- Application June 8, 1934, Serial No. 729,583

7 Claims.

This invention relates to an improved method of hardening of steel, and is particularly :adapted to the hardening of steel wire.

An object of this invention is to simplify and 5 improve the method of controlling the hardening of steel wire by keeping the temperature of the wire to be hardened substantially constant.

Another object of this invention is to produce a steel wire which is tempered extremely uniform throughout its entire length, which results in a more uniform product. rlhe hardening of steel wire is well known in the art, there being nui-nerous methods and processes. However, there is not known any simple method or system of which applicant is aware, that will produce a wire which is uniformly tempered throughout its entire length.

In the hardening process of steel wire :according to this invention, the wire is hardened at a 24) uniform temperature by a simple method of accurately controlling the temperature ofthe steel wire just before it is chilled. The underlying principle of this invention is an electrical system comprising electron discharge devices and associated inductance coils through which the wire passes. The wire when passing through the inductance coils acts as a core to vary the inductance, the change of the inductance in the coils being due to the permeability of the wire changing with the fluctuations in temperature which is used to control the temperature and maintain it uniform just before quenching in the cooling bath. The invention makes use of the change in permeability of the wire at the recalescence temperature to vary the inductance coli as it passes through its center.

The invention will be more clearly understood by referring to the accompanying drawing in which the wire i to be tempered passes over a 40 roller 2 into a primary heating oven 3 and then through the center of a reactance coil Il where it is then led into the secondary heating oven from which the wire passes over a roller 6 and into the cooling tank l which contains the desired 45 cooling or quenching liquid 8, such as oil, water, mercury, or any other suitable liquid. The wire passes through the cooling tank and under the submerged roller 9, and then over the roller iii from which it is then wound upon any desired form of spool.

Referring now in detail to the drawing, the temperatureof the wire to be hardened is raised and then maintained constant by means of an electrical power input I I which supplies energy to the electric heaters I2, I3 and I4.

(Ci. B19- lll The functions of the three heaters are as follows: Heater I4 is of large size and considerable length. Its purpose is to raise the wire temperature to a point a little below the recalescence temperature. Its temperature and the tempera-- ture to which it raises the wire may be manually adjusted. Heater I3 is smaller and shorter than heater I4, and ls provided with automatically controlled temperature for holding the wire just before going through the reactance coil very accurately at the recalescence temperature. Heater I2 is designed to raise the wire temperature slightly above its normal recalescence temperature than when it passed through the reactance coil in order to obtain just the right desired temperature for quenching.

Due to the need of a very accurate control of the ingoing wire temperature, heater I2 may if desired be manually adjusted byany suitable resistance means, not

shown. Associated with the heaters are transformers I5 and I6, and a rectifier I 'I which is connected in a bridge-like arrangement. The output of the secondary of the transformer i5 is connected to the plates of a pair of electronic discharge tubes or thyratrons i8 and i9 which consist of evacuated containers enclosing the cathodes, grids, anodes, and an inert gas. A thyratron of this construction has such properties that if the grid is maintained suiciently negative, an

anode current will not dow unless a critical value of positive potential on the anode electrode is exceeded. However, if the anode electrode is positively charged beyond the c ritical point determined by the grid bias potential, current will commence to ow, and having once started to flow, will continue flowing until the positive poiarization or charge is removed from the anode electrode. As the anode becomes positive on each alternate haii cycle of the applied alternating current anode voltage the time on the potential wave at which current starts tc flow is determined by the grid potential.

Therefore the total or average flow of current may be readily ccntrolled by variations in the grid potential. After once starting the arc the ilow or continuation thereof cannot be aected by the grid. However, it can be stopped by the removal or reversal of the anode voltage which occurs once each cycle of the impressed alternating current anode voltage. Thus it will be seen that such a type of tube operates as an intermittent arc discharge device whose average current ow is controlled by its grid.

tron type of electron discha.

rge device may be obtained by referring to an article by A. W. Huil, appearing on page 390 of the General Electric Review for July, 1929 (vol. 32, No. '7).

The cathodes of both electron discharge tubes are heated by the secondary of transformer 22, and the voltage of the primary is controlled by a rheostat 23. 'I'he input voltage I I supplied to the reactance controlling coil 4 is applied through the reslstances 20 and 2I.

In the operation of this invention the wire I which is to be hardened, passes over the roller 2 into the primary heating oven 3, and is heated by means of the large heating unit I4. It then passes through the automatically controlled small heater I3 whose heating current consists of the direct current or rectified component of current through the tubes I8 and I9. The heated wire which has been heated to the recalescence temperature, then passes through the reactance or heat control coil 4; the wire so passing acts as the core for the reactance coil. As the temperature of the wire changes, the reactance of the inductance coil 4 increases as the wire temperature drops below the recalescence temperature and decreases when the temperature rises above the recalescence temperature. The variation in reactance varies the voltage drop across the reactance coll. This voltage is rectied by rectier I1 which is preferably of the oxide type, and used to control the grid bias potential on the thyratrons I1 and I8.

If the wire passing through the reactance coil has a temperature slightly below the recalescence temperature, it will have a relatively high magnetic permeability and give the coil a large reactance.- This increases the voltage drop acrossthe coil and, through the rectiers, drives the thyratron grids positive. 'I'his in turn increases the power applied to heater I3 and raises the wire temperature. If the wire temperature is too high the wire loses its magnetic permeability, the coil reactance diminishes, the thyratron grids become less positive, and the power input to heater I3 is diminished. Thus the temperature' of. the wire through the reactance coil is held very accurately at a point Where the magnetic permeability vanishes and reappears. This is known in the art as the recalescence temperature.

The g'ure shows only one very simple arrangement for practicing my invention. Obviously many additional features may be added in accordance with arts well known in the electrical and. metallurgical fields. As examples of modications the following may be noted:-

(a) Electrical regulating devices and measuring instruments may be added to the circuits.

(b) The heating of the wire may be done in reducing atmospheres, such as hydrogen, for preventing deterioration or oxidation of the wire heaters, reactance coil, etc.

(c) All or a portion of the heating may be done ln atmospheres containing carbon or other elements for case hardening the wire or for modifying the properties of the surface in any other way.

A(d) The rollers shown in the cooling tank may be eliminated or altered to prevent undesirable bending of the wire by arranging the assembly vertically instead of horizontally as shown.

(e) A part or all of the heating may be done by other means than electricity. For example, gas heating, electrically controlled by the thyratron current may be used.

(f) The thyratrons may be replaced with high vacuum tubes, relays, or any other suitable electrical control device.

(g) In some cases the cooling bath may be such materials as molten lead, tin, zinc, cadmium, or metal alloys and mixtures. If the finished product is to be coated with zinc, for example, the use of a zinc cooling bath will automatically result in the production of a coating roughly equivalent to galvanizing or shearardizing.

(h) Automatic tensioning, measuring and speed control devices may be added to the equipment.

(i) 'I'he reactance which is varied by the variation in magnetic permeability of the wire around its recalescence temperature need not be a coil about the wire, but may be any arrangement in which a portion of the wire forms a part of a magnetic circuit interlinking a coil.

`(j) In addition to controlling the heat by means of the variable reactance coil the speed with which the wire is drawn througlr the hardening apparatus may be varied automatically by automatically varying the power input to the pulling apparatus as well asto the heater.

(1c) Between the controlled heater and the variable reactance there may be a space over which the wire temperature is dropping. 'Ihis permits the wire to be heated considerably above the recalescence temperature, cooled down to the recalescence temperature for accurate control, reheated somewhat above the recalescence temperature and then quenched. This corresponds to the heat treatment required for desired results in some steel wire products.

While this invention has been described as being used for controlling the temperature of steel Wire, it is to be understood that its limitations are to be only those imposed by the appended claims.

What is claimed is:

1. In a system wherein a steel wire is heated prior to being hardened, comprising means for moving said wire, means for heating and controlling the temperature to maintain a constant value of heat on said wire, said means comprising a first heater, a second heater, and a reactance coil, all of which surround said wire, a source of alternating current connected to said rst heater, means for connecting said alternating current to said reactance coil, means for obtaining a voltage drop across said reactance coil as the wire moves through said coil in accordance with the permeability of the wire as inuenced by the temperature thereof, a rectier having its input coupled to said reactance coil to rectify said voltage drop, an electron discharge device having an anode, grid and cathode, means for maintainingsaid cathode in an electron emitting condition, means for keeping the temperature of said wire at a desired constant temperature as it passes through said second heater, said means comprising a circuit connection from the output of said rectifier to the grid circuit of said electron discharge device, and a circuit connection from the anode circuit of said electron discharge device to said second heater whereby the grid bias potential of said electron discharge device is altered by variationsin the permeability of the steel wire as it passes through said reactance coil to thereby control the temperature of said second heater.

2. In a system wherein a steel wire is heated prior to being hardened comprising means for moving said wire, means for heating and controlling the temperature to maintain a constant value of heat on said wire, said means compris- .ing a tix-st heater, a second heater, and a reactance coil, all of which surround said wire, a source of alternating current connected to said iirst heater, means for connecting said alternating current to said reactance coil, means for obtaining a voltage drop across said reactance coil as the wire moves through said coil in accordance with the permeability oi the wire as influenced by the temperature thereof, a rectifier having its input coupled to said reactance coil to rectify said voltage drop, a pair of electron discharge devices each. having an anode, grid and cathode, means for maintaining said cathodes in an electron emitting condition, means for keeping the temperature of said wire at a desired constant temperature as it passes through said second heater, said means comprising a circuit connection from the output of said rectifier to the lgrid circuit of said electron discharge devices, and e circuit connection from the anode circuit of said electron discharge devices to said second heater whereby the grid bias potential of said electron discharge devices is altered by variations in the permeability ci? the steel wire as it passes through said reactance coil to thereby control the temperature oi said second heater.

3. in a system wherein a 'steei Wire is heated prior to being hardened comprising means for moving said wire, means for heating and coritrolling the temperature to maintain a constant value or heat on said wire, said means comprising a nrst heater', a second heater, and a reactance coil, all oi which surround said wire, a source oi` alternating current connected to said rst heater, means for connecting said alternating current to said reactance coii, means for obtaining a voltage drop across said reactance coil as the voire moves through said coii in accordance with the permeability of the wire as inuencecl by the temperature thereof, a rectider having its input coupled to said reactance coii by a transformer to rectiy said voltage drop, an electron discharge device having an anode, grid and cathode, means for maintaining said cathode in an electron emitting condition, means tor keeping the temperature of said Wire at a desired constant temperature as it passes through said second heater, said means comprising a circuit connection from the output oi said rectifier to the grid circuit or' said eiectron discharge device, and a circuit connection from the anode circuit of said electron discharge device to said second heater whereby the grid bias potential of said electron discharge device is altered by variations in the permeability or the steel Wire as it gasses through said reactance coil to thereby controi the temperature of said second heater.

4. In a system wherein a steel wire is heated prior to being hardened comprising means for moving said wire, means for heating and controlling the temperature to maintain a constant value of heat on said Wire, said means comprising a rst heater, a second heater, and a reactance coil, all of which surround said wire, a source of alternating current connected to vsaid first heater, means for connecting said alternating current to said reactance coil, means for obtaining a voltage drop across said reactance coil as the wire moves through said coil in accordance with the permeability of the wire as in'- uenced by the temperature thereof, a rectifier comprising a plurality of rectifier units being connected in a bridge-like arrangement, said rectifier having its input coupled to said reactance coil by a transformer to rectify said voltage drop, an electron discharge device having an anode, grid and cathode, means for maintaining said cathode in an electron emitting condition, means for keeping the temperature of said wire at a desired constant temperature as it passes through said second heater, said means comprising a circuit connection from the output of said rectier to the grid circuit of said electron discharge device, and a circuit connection from the anode circuit of said electron discharge device to said second heater whereby the grid bias potential of said electron discharge device is altered by variations in the permeability of the steel wire as it passes through said reactance coil to thereby control the temperature of said second heater.

5. In a system wherein a steel Wire is heated prior to being hardened comprising means for moving said wire, means for heating and controlling the temperature to maintain a constant value of heat on said Wire, said means comprising a iirst heater, a second heater, anda reactance coil, all of which surround said wire, a source of alternating current connected to said first heater, means for connecting said alternating current to said reactance coil, means for obtmlning a voltage .drop across said reactance coil as the wire moves through said coil in accordance with the permeability of the Wire as inliienced by the temperature thereof, a rectifier having its input coupled to said reactance coil to rectify said voltage drop, an electron discharge device having an anode, grid and cathode, means for maintaining said cathode in an electronA emitting condition, means for keeping the temperature or said wire at a desired constant temperature as it passes through said second heater, said means comprising a circuit connection from the output of said rectifier to the grid circuit of said electron discharge device, a circuit connection from the anode circuit of said electron discharge device to said second heater whereby the grid bias potential of said electron discharge device is altered by variations in the permeability of the steel Wire as it passes through said reactance coil to thereby control the temperature of said second heater, and a third heater surrounding said wire, said third heater being connected to said alternating current to slightly raise the temperature o said wire to a desired constant value prior to quenchmg.

6. in a system wherein a steel wire is heated prior to being hardened comprising means for moving said wire, means for heating and controlling the temperature to maintain a. constant value of heat on said wire, said means comprising primary and secondary heating ovens, said primary heating oven having contained therein e. rst heating coil of considerable length and a second heating coil shorter in length than said rst heating coil, a reactance coil located between said primary and secondary heating ovens, all of said coils surrounding said wire, a source oi' alternating current connected to said first heating coil, means for connecting said alternating current to said reactance coil, means for obtaining a. voltage drop across said reactance coil as the wire moves through said coil in accordance with the permeability of the wire as influenced by the temperature thereof, a, rectifier Ahaving .its input coupled to said reactance coil to rectify said voltage drop, an electron discharge device having' an anode, grid and cathode, means for maintaining said cathode in an electron emitting condition, meansl for keeping the temperature of said wire at a desired constant temperature as it passes through said second heating coil, said means comprising a circuit connection from the output oi said rectitler to the grid circuit of said electron discharge device, a circuit connection from the anode circuit of said electron discharge device to said heating coil whereby the grid bias potential of said electron discharge device is altered by variations in the permeability of the steel wire as it passes through said reactance coil to thereby control the temperature of said second heating coil, and a third heating coil surrounding said wire and located in said secondary oven, said third heating coil connected to the alternating current to slightly raise the temperature of the wire to a desired constant value prior to quenching.

7. In a *system wherein steel strip material of substantially continuous length is heated prior to being hardened comprising means for moving said strip, means for heating and controlling the temperature to maintain a constant value of the heat on said strip, said means comprising a first heater, a second heater, and a reactance amarre coil, all .of which surround said strip, a source of alternating current connected to said rst heater, means for connecting said alternating current to said reactance coil, means for obtaining a voltage drop across said reactance coil as the strip moves through said coil in accordance with the permeability of the strip as inuenced by the temperature thereof, a rectier having its input coupled to said reactance coil to rectify said Voltage drop, an electron discharge device having an anode, grid and cathode, means i'or maintaining said cathode in an electron emitting condition, means for keeping the temperature of said strip at a desired constant temperature as it passes through said second heater, said means comprising a circuit connection from the output of said rectier to the grid circuit of said electron discharge device, and a circuit connection from the anode circuit of said electron discharge device to said second heater whereby the grid bias of said ele'ctron discharge device is altered by variations in the permeability of said steel strip as it passes through said reactance coil to thereby control the temperature of said second heater.

CLARENCE W. HANSELL. 

